The Long Term Evolution (LTE) system deployed by the 3rd Generation Partner Project (3GPP) is intended to provide increasingly diversified mobile communication services in the future. Wireless cellular communications have become an essential part of people's lives and work. In the first release (Release 8) of the 3GPP LTE, Orthogonal Frequency Division Multiple Access (OFDMA) and Multiple Input Multiple Output (MIMO) techniques have been introduced. After evaluation and test by International Telecommunication Union (ITU), the 3GPP Release 10 has been established as the 4th generation global mobile communication standard, known as LTE-Advanced. In the LTE-Advanced standard, Carrier Aggregation (CA) and relay techniques have been introduced to improve uplink (UL)/downlink (DL) MIMO technique while supporting heterogeneous network (HetNet) deployment.
In order to meet the market demand on home device communications and the deployment of a huge-scale Internet of Things (IoT) in the future, the 3GPP has decided to introduce a low-cost Machine Type Communication (MTC) technique in the LTE and its further evolution, to transfer MTC services from the current GSM network to the LTE network and define a new type of User Equipment (UE), referred to as Low-cost MTC UE. Such UE can support MTC services in all duplex modes in the current LTE network and has: 1) one single receiving antenna; 2) a maximum Transport Block Size (TBS) of 1000 bits in UL/DL; and 3) a reduced baseband bandwidth of DL data channel of 1.4 MHz, a bandwidth of DL control channel identical to the system bandwidth of the network layer, and the same UL channel bandwidth and DL Radio Frequency (RF) part as UEs in the current LTE network.
The MTC is a data communication service without human involvement. A large-scale deployment of MTC UEs can be applied to various fields such as security, tracking, payment, measurement, consumer electronics, and in particular to applications such as video surveillance, supply chain tracking, intelligent metering and remote monitoring. The MTC requires low power consumption and supports low data transmission rate and low mobility. Currently, the LTE system is mainly designed for Human-to-Human (H2H) communication services. Hence, in order to achieve the scale benefit and application prospect of the MTC services, it is important for the LTE network to support the low-cost MTC devices to operate at low cost.
Some MTC devices are mounted in basements of residential buildings or locations protected by insulating films, metal windows or thick walls of traditional buildings. These devices will suffer significantly higher penetration loss in air interface than conventional device terminals, such as mobile phones and tablets, in the LTE network. The 3GGP has started researches on solution designs and performance evaluations for the LTE network to provide the MTC devices with a 20 dB of additional coverage enhancement. It is to be noted that an MTC device located in an area with poor network coverage has a very low data transmission rate, a very loose delay requirement and a limited mobility. For these MTC characteristics, some signaling and/or channels of the LTE network can be further optimized to support the MTC. The 3GPP requires providing the newly defined low cost UEs and other UEs running MTC services (e.g., with very loose delay requirements) with a certain level of LTE network coverage enhancement. In particular, a 15 dB of network coverage enhancement is provided in the LTE Frequency Division Duplex (FDD) network. Additionally, not all UEs running MTC services need the same network coverage enhancement.
For the new low-cost MTC devices, in the DL, the data channel is 1.4 MHz (i.e., 6 RBs) and the control channel can still access the entire DL system bandwidth in the baseband part, while the RF link part remains the same, i.e., the entire system bandwidth can be accessed. In the UL, the baseband part and the RF part both remain the same. In addition, the low-cost MTC UE has one single receiving antenna and its maximum UL transport block and DL transport block are each 1000 bits.
For 3GPP LTE UEs running MTC services in the coverage enhancement mode, the design and configuration of coverage enhancement for physical channels (such as Physical Downlink Control Channel (PDCCH), Physical Downlink Shared Channel (PDSCH), Physical Uplink Control Channel (PUCCH) and Physical Uplink Shared Channel (PUSCH)) need to be standardized. According to the discussions in the 3GPP RAN1 #74 meeting, after completion of the initial access, the configuration mode of any physical channel that requires repetitive transmission is decided at the base station. In the discussions in the 3GPP RAN1 #75 meeting, for an MTC UE in the coverage enhancement mode, its UE specific search space supports PDSCH scheduled by (E)PDCCH (i.e., PDCCH and/or Enhanced PDCCH) and supports a number of repetitive transmission levels for (E)PDCCH. From the perspective of UE, the potential start subframe of the repetitive transmission of (E)PDCCH should be limited to a certain set of subframes. The LTE does not support periodical repetitive transmission of CSI in PUCCH, but supports repetitive transmission of ACK/NACK in PUCCH and a number of repetitive transmission levels for PDSCH/PUSCH in time domain.
When a UE in the coverage enhancement mode runs an MTC application service, the PDCCH requires repetitive transmission in a number of subframes.